This program is designed to provide a multifaceted approach to the study of the physiological significance of in vitro blood rheology studies. The long range goal of the proposed research is to contribute to the understanding of the relation of the rheological properties of blood to: 1) the flow of blood in vivo; 2) the diagnosis and treatment of clinical disorders associated with potential rheological alterations. The specific aims of the present program include: 1) studies of the flow behavior of various erythrocyte suspensions in narrow bore glass tubes having geometries relevant to the microcirculation; 2) physical- hemorheological analyses of the effects of liquid storage of human blood intended for transfusion, including macro- and micro- rheologic studies and the evaluation of potassium-containing storage media; 3) continue studies of specific erythrocyte cellular factors which influence erythrocyte aggregation and thus to explore possible reasons for differences in aggregation noted between young and old red cells and between red cells from normal donors; 4) hemorheological evaluation of blood, red cells and white cells from patients whose clinical state is characterized by altered rheological properties of blood (i.e., acute cerebral ischemia, diabetes mellitus, acute myocardial infarction). Successful completion of the major aims of this program should provide: 1) quantitative information relevant to the prediction of pressure- flow relations in a vascular bed based on in vitro rheologic data; 2) additional insight into the mechanisms involved in red cell aggregation; 3) detailed data regarding the macro- and micro- rheological properties of stored and pathologic blood. Of long range significance is the potential contribution which studies of this type may make to clinical medicine: if syndromes of "hyperviscosity" are to be utilized with scientific meaning, a clearer understanding of their etiology, rheologic mechanisms and physiological import is essential.